Inverted Polarity of tube Pre-Amps - diyAudio
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Old 26th September 2012, 10:44 PM   #1
kach22i is offline kach22i  United States
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Default Inverted Polarity of tube Pre-Amps

When I purchased my GRAAF WFB ONE pre-amp about eight years ago, the seller told me that the output has switched "polarity", and that I should invert my speaker wires or invert my output interconnects (but not both at the same time).

That is to say put R to L and L to R.

However, I have just re-tubed the unit and nothing in the owner's manual mentions reversed polarity.

In fact it says: Connect the input and output pins to the LEFT and RIGHT channels respecting the signal direction. Assure that the connections are good.

Was I given bad information by the stereo shop which sold me my unit, or is the manual a bit neglectful?

Is there a simple way to test the polarity of my unit?
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Old 26th September 2012, 10:50 PM   #2
tomchr is online now tomchr  United States
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Switched polarity probably refers to that the preamp is inverting. I.e. the output is 180 degrees out of phase with the input. You should swap the (+) and (-) terminals on the speaker cables not L and R.

The best way to ensure that you have the correct signal polarity is to perform an end-to-end measurement of the system's impulse response. This requires a measurement microphone, computer sound card with MIC input, and some software (FuzzMeasure on Mac, HolmImpulse on Windoze).

~Tom
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Old 26th September 2012, 10:55 PM   #3
kach22i is offline kach22i  United States
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Quote:
Originally Posted by tomchr View Post
The best way to ensure that you have the correct signal polarity..........
Tom, that sounds a bit more involved than I initially wanted to invest.

I have a few test CD's somewhere, maybe I can find them and finally put them to use.

My main concern was the possibility of doing damage to my equipment. This is not a concern, right?

This looks interesting, has anyone tried it?

https://groups.google.com/forum/?fro...on/q4QKKlpHMM8
Quote:
Get the recording of Rickie Lee Jones first album, called,
appropriately, Rickie Lee Jones. Listen to the track EASY MONEY. With a
system that is correct in absolute phase, she sounds like she is in fornt
of the instruments (naturally!) and when the system inverts, she sounds
like she is behind the insstruments. There are many other recordings
where this effect is easily heard.
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Last edited by kach22i; 26th September 2012 at 11:04 PM.
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Old 26th September 2012, 11:16 PM   #4
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If it sounds OK do nothing. If it sounds bad (lack of bass, bad stereo image) swap + and - on one speaker.

But like Tom said, the seller probably refered to a phase shift. Even then it would make no sense to swap wires or interconnects.
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Old 27th September 2012, 12:11 AM   #5
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A lot of source material out there is inverted in polarity. So does it really matter? Well sometimes...
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Old 27th September 2012, 12:25 AM   #6
tomchr is online now tomchr  United States
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Quote:
Originally Posted by kach22i View Post
My main concern was the possibility of doing damage to my equipment. This is not a concern, right?
There is no harm done in connecting an inverting preamp to a regular power amp and speakers without swapping any wires.

~Tom
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Old 27th September 2012, 10:42 AM   #7
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My understanding is that some people can detect absolute phase on some programme material. Most people can't detect it on any material. Most recording/broadcast chains make no effort to maintain phase, so if it affects you then you will have to detect and note the correct setting for each piece of music.

I hope the original LR vs. +- confusion was down to you and not the shop salesman!
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Old 27th September 2012, 02:46 PM   #8
kach22i is offline kach22i  United States
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Thanks everyone, I had just replaced the tubes in my pre-amp but not the ones in the phono section, and I have the same problem I had before (inverted polarity aside).

Guess it wasn't the tubes gone bad after all.

I'm getting sound out of the left speaker only, the balance control seems to have no effect (some volume fluctuation). When I turn it all the way to the right, sound still only comes out of the left.

I'm guessing it could be the balance potentiometer, but really don't have an idea, just guessing.

I'll double check any possible physical or mechanical linkages which may or may not exist between the channels.

Looks like the pre-amp is going to the shop with the in need of repair tube power amp I have.
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